2.3 Microwave-assisted fractionation and functionalization of Kraft lignin for the production of bio-based thermosets

Petroleum-based aromatic compounds are commonly used in industries to produce rigid and thermally stable materials as a result of the few green alternatives able to provide the same chemical and mechanical properties. Lignin represents the most promising source of aromatic natural polymers deriving from wood biomass. However, its heterogenous structure makes it an inconsistent and low-reactivity precursor. Therefore, in this project, fractionation of softwood LignoBoost Kraft lignin (KL) is performed using microwave-assisted technique in order to produce narrow-dispersity and low molecular weight oligomers. Once lignin fractions are obtained, hydroxyl groups are targeted for functionalization through microwave-assisted allylation. Combination of spectroscopy techniques allows to provide a detailed description of the technical lignin structures before and after the reaction. Moreover, morphological properties are investigated using Scanning electro microscope. Allylated lignin is subsequently crosslinked through thermally induced thiol-ene chemistry in order to produce fully bio-based thermosets. Afterwards their thermal and mechanical properties are analyzed using micro indentation hardness testing.